The Guianan Highlands Moist Forests: A Tapestry of Rainforests and Savannas on the Ancient Guiana Shield

Nestled within the heart of northern South America, the Guianan Highlands moist forests ecoregion stands as a unique and captivating landscape, distinct from the surrounding Amazonian ecoregions. This montane region, encompassing portions of southern Venezuela, western and southern Guyana, northern Brazil, and scattered areas of Suriname, French Guiana, and eastern Colombia, is a mosaic of towering primary rainforests, open semi-treeless savannas, and gallery forests that wind their way through the rugged terrain. Sitting atop the ancient Guiana Shield, this ecoregion is a testament to the geological forces that have shaped the region over millions of years, creating a diverse and remarkable ecosystem that harbors a wealth of biodiversity.

Geographic Setting and Geology

The Guianan Highlands moist forests ecoregion lies predominantly within the eastern portion of the Orinoco Basin, which drains into the Caribbean Sea from Venezuela. However, a portion of the ecoregion also extends into the Amazon Basin, with rivers like the Rio Uraricuera and Rio Branco flowing into the mighty Amazon.

Underlying this ecoregion is the ancient Guiana Shield, a vast expanse of rock basement formed from various igneous and metamorphic rocks during different geological events. The upland terraces and mountains that characterize the Guianan Highlands are remnants of highly weathered and ancient parent material, primarily quartzite or sandstone rocks. However, granitic rock types persist in some areas.

Climate and Hydrology

The climate of the Guianan Highlands moist forests ecoregion is seasonal. It is humid to sub-humid and characterized by evenly distributed rainfall ranging from 2,000 to 2,400 millimeters (78 to 95 inches) annually. The average annual temperature hovers around 24°C (75°F), providing ideal conditions for the lush vegetation that thrives in this region.

Major rivers originating from the ecoregion and feeding into the Orinoco Basin include the Orinoco headwaters, the Ventuari, Caroní, Paragua, and Caura in Venezuela. In the southern portions, the Rio Uraricuera and Rio Branco drain into the Amazon Basin, contributing to the vast waterways sustaining the region's diverse ecosystems.

Flora and Fauna

The Guianan Highlands moist forests boast an impressive biodiversity, with over 200 mammal species, many of which are widespread Amazonian species such as jaguars (Panthera onca), pumas (Puma concolor), tapirs (Tapirus terrestris), two species of peccaries (Tayassu pecari and T. tajacu), and various deer species (Mazama spp.). Additionally, the ecoregion is home to endemic species like the olingo (Bassaricyon beddardi) and several endemic rodents, including Sciurus flammifer, Proechimys hoplomyoides, and Dasyprocta guamara.

The avian diversity is equally remarkable, with over 600 species recorded, including several endemic and restricted-range species. Notable birds found in the ecoregion include the white-cheeked pintail (Anas bahamensis), aplomado falcon (Falco femoralis), brown-throated parakeet (Aratinga pertinax), pavonine cuckoo (Dromococcyx pavoninus), vermiculated screech owl (Otus guatemalae), burrowing owl (Athene cunicularia), various emerald and hummingbird species from the Amazilia genera, chestnut-tipped toucan (Aulacorhynchus derbianus), smoke-colored pewee (Contopus fumigatus), orange-crowned oriole (Icterus auricapillus), gray seedeater (Sporophila intermedia), two-banded warbler (Basileuterus bivittatus), and black-backed water-tyrant (Fluvicola albiventer).

Reptiles and amphibians are abundantly represented in the Guianan Highlands moist forests, with iconic species such as the fer-de-lance (Bothrops asper), palm pit-vipers (Bothriechis spp.), coral snakes (Micrurus spp.), boa constrictors (Boa constrictor), bushmasters (Lachesis muta), iguanas (Iguana iguana), and tegus lizards (Tupinambis) inhabiting the diverse habitats of the ecoregion.

Conservation Status and Threats

While many of the interior forests of the Guianan Highlands moist forests ecoregion remain intact, threats from large-scale agriculture, mining, and cattle raising are encroaching upon the northern and northeastern periphery of the region, nearest to urban centers. Recently, these impacts have begun to extend further into the heart of the ecoregion, underscoring the need for concerted conservation efforts.

Several notable protected areas have been established within or encompassing portions of this ecoregion, including the Alto Orinoco-Casiquiare Biosphere Reserve, Canaima National Park, Parima-Tapirapecó National Park, Serranía La Neblina National Park, and Pico da Neblina National Park. These protected areas aim to safeguard the unique biodiversity and ecological integrity of the Guianan Highlands moist forests, ensuring that this remarkable ecosystem can continue to thrive for generations.

_{Map depicting the location of the Guianan Highlands moist forests ecoregion (in purple).}